Growth hormone releasing hormone (GHRH) is a member of a family of related gut, brain and gonadal peptides that includes PACAP and VIP. All the genes in this family produce two or more biologically active peptide products except for GHRH, which is known to make only one functionally significant peptide. The applicant recently discovered that the GHRH gene actually produces two distinct peptides: GHRH and a novel C-terminal peptide, the applicant has called GHRH-related peptide (GHRH-RP). GHRH-RP immunoreactivity was found to be abundant in hypothalamus and testes, two tissues which also produce GHRH. In testes GHRH-RP acts to stimulate the expression of stem cell factor (SCF), a sertoli cell products required for normal spermatogenesis. This proposal is deigned to initiate characterization of this newly described peptide product. The applicant proposes to determine the general tissue distribution of GHRH-RP by immunoassay, immunohistochemistry, and Western blot analysis. The binding characteristics of GHRH-RP to Sertoli cells will be studied by radioreceptor assay and in vitro autoradiography. The intracellular signaling pathways activated by GHRH-RP will be evaluated and using molecular cloning techniques the GHRH-RP receptor will be cloned. Finally the role of GHRH-RP in the paracrine regulation of spermatogenesis will be determined.